The present invention relates to printing devices. More particularly, the present invention relates to an apparatus and method of compensating for print engine expansion or contraction in a printing device.
Printing devices, such as inkjet printers and laser printers, include print engines that use printing composition (e.g., ink or toner) to print images (text, graphics, etc.) onto a print medium in a printzone of the printing device. Inkjet printer print engines may use print cartridges, also known as "pens", which shoot drops of printing composition, referred to generally herein as "ink", onto a print medium such as paper, transparency or cloth. Each pen typically has a different color ink, such as cyan, magenta, yellow or black, and a printhead that includes a plurality of nozzles. Each nozzle has an orifice through which the drops are ejected. To print an image, each printhead is propelled back and forth across a print medium along a scan axis by, for example, a carriage of the print engine while ejecting drops of ink in a desired pattern as the printhead moves. Each pen is disposed in the carriage a distance apart from any other pens. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as thermal printhead technology. For thermal printheads, the ink may be a liquid, with dissolved colorants or pigments dispersed in a solvent.
In a current thermal system, a barrier layer containing ink channels and vaporization chambers is located between an orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heating elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, the ink in the vaporization chamber turns into a gaseous state and forces or ejects an ink drop from a orifice associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the print medium, the ink is expelled in a pattern onto the print medium to form a desired image (e.g., picture, chart or text).
In order to help optimize the appearance of printed images, the individual pens are aligned so that the different colored drops of ink ejected therefrom are placed onto a print medium at the desired location. Such pen-to-pen alignment is typically done through the use of a test pattern that is printed and then measured by a sensor or judged by a user.
Print engines of printing devices, such as inkjet printers, often depend on a linear displacement optical encoder to trigger the firing of the pens as well as to provide feedback for position and velocity of the carriage holding the pens. The optical encoder may be made from things such as photo imaged MYLAR brand film. The optical encoder works with a light source and a light detector, both of which are typically mounted on the carriage. The light source directs light through the encoder which is received by the light detector and converted into an electrical signal which is used by electronics of the printing device to control firing of the pens, as well as carriage position and velocity. Markings or indicia on the encoder periodically block this light from the light detector in a predetermined manner which results in a corresponding change in the electrical signal from the detector.
During operation of the printing device, ambient temperature and humidity may change. Such changes may cause the encoder and one or more elements of the print engine, such as the carriage, to expand or contract depending on whether temperature and humidity are increasing or decreasing. As the carriage expands or contracts in the scan axis direction with changes in ambient temperature or humidity, the pen-to-pen distance will change. If the encoder expands or contracts at the same rate as the carriage, the effective resolution of the printer will shift, but the pens will stay in alignment. If the carriage and encoder expand or contract at different rates, however, the pens will no longer be aligned and output print quality of the printing device will likely be degraded.
An apparatus and method that solved the above-described problems associated with print engine and encoder expansion or contraction would be a welcome improvement. Accordingly, the present invention is directed to compensating for print engine and encoder expansion or contraction to help maintain alignment of the print elements of the print engine.
An embodiment of an apparatus in accordance with the present invention for use in a printing device, the printing device including a print engine and an encoder that indicates where the print engine should print on a print medium, includes a first target on the encoder and a second target on the encoder. The apparatus also includes a first sensor configured to output a first signal upon detection of the first target and a second sensor configured to output a second signal upon detection of the second target. The apparatus additionally includes a computing device coupled to the first sensor to receive the first signal, the second sensor to receive the second signal, and the print engine. The computing device is configured to determine a difference between receipt of the first signal and the second signal, and the computing device is further configured to adjust when the print engine prints on the print medium based on this difference.
The above-described embodiment of an apparatus in accordance with the present invention may be modified and include at least the following characteristics, as described below. The first target and the second target may be formed through the encoder. The encoder may be a substantially rectangular strip.
The first sensor and the second sensor may be positioned on the print engine. The print engine may include a carriage and at least one inkjet printhead disposed on the carriage. In such cases, the first sensor and the second sensor may be positioned on the carriage.
An alternative embodiment of an apparatus in accordance with the present invention for use in a printing device, the printing device including a print engine and an encoder that indicates where the print engine should print on a print medium, includes structure for measuring a difference between an amount of expansion of the print engine during printing and an amount of expansion of the encoder. The apparatus additionally includes structure for adjusting a time when the print engine prints on the print medium based on the determined difference.
An embodiment of a method in accordance with the present invention for use in a printing device, the printing device including a print engine and an encoder that indicates where the print engine should print on a print medium, includes measuring a difference between an amount of expansion of the print engine during printing and an amount of expansion of the encoder. The method additionally includes adjusting a time when the print engine prints on the print medium based on the determined difference.
The above-described embodiment of a method in accordance with the present invention may be modified and include the following characteristics, as described below. The method may include aligning image data printed on the print medium by the print engine. The print engine may include a carriage and at least one inkjet printhead disposed on the carriage.
The foregoing summary is not intended by the inventor to be an inclusive list of all the aspects, advantages, and features of the present invention, nor should any limitation on the scope of the invention be implied therefrom. This summary is provided in accordance with 37 C.F.R. Section 1.73 and M.P.E.P. Section 608.01(d). Additionally, it should be noted that the use of the word substantially in this document is used to account for things such as engineering and manufacturing tolerances, as well as variations not affecting performance of the present invention. Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.